1. Field of the Invention
The present invention relates to a signal transmission system, a signal transmission apparatus, and a signal reception apparatus, which are able to transmit or transmit and receive an audio signal and a control signal together with a video signal.
2. Description of the Related Art
A conventional signal transmission system based on the Digital Visual Interface (DVI) standard will be described with reference to FIG. 25. FIG. 25 is a block diagram illustrating the construction of the conventional signal transmission system.
In FIG. 25, the conventional signal transmission system comprises Transmission Minimized Differential Signaling (TMDS) encoders/serializers 2601˜2603 which are provided on the transmitting end, and TMDS decoders/recovery units 2604-2606 which are provided on the receiving end.
In the conventional signal transmission system, video signals such as RED, GREEN, and BLUE are inputted to the TMDS encoders/serializers 2601˜2603 at the transmitting end, and the TMDS encoders/serializers 2601˜2603 perform TMDS encoding on the video signals, serialize the encoded video signals, and output the serialized video signals to a transmission path. At the receiving end, the TMDS decoders/recovery units 2604˜2606 perform TMDS decoding on the received signals, and recover the decoded signals to restore the video signals.
A Data Enable (DE) signal is a signal indicating a period during which a video signal such as RED, GREEN, or BLUE exists, and this is a HIGH active signal. For example, a period during which the DE signal is LOW is a horizontal blanking period or vertical blanking period of the video signal. Four control (CTL) signals, CTL0, CTL1, CTL2, and CTL3, are prepared as control signals. However, in the existing DVI standard, these CTL signals are not used yet. To be specific, the levels of these control signals are “0” at all times.
In each of the TMDS encoders/serializers 2601˜2603 at the transmitting end, a video signal inputted by 8 bits is converted into a 10-bit video signal, and serialized to be outputted to the transmission path. The purpose of the 8-bits/10-bits conversion is to convert the video signal into a form suited for high-speed transmission by reducing the change points of data. Further, in the TMDS encoders/serializers 2601˜2603, a 2-bit control signal is converted into a 10-bit control signal to be outputted to the transmission path. Further, the DE signal is also encoded, serialized, and outputted to the transmission path. In each of the TMDS decoders/recovery units 2604˜2606 at the receiving end, the 10-bit serial data received from the transmission path is decoded and recovered to the 8-bit chrominance signal, the DE signal, and the 2-bit control signal.
Since the DVI standard is a standard for transmitting only video signals (R, G, B signals), the conventional signal transmission system cannot transmit an audio signal and a control signal to be used for controlling a monitor or the like.
Furthermore, also in the case where a video signal is transmitted using a standard other than the DVI standard, a video signal and an audio signal or a control signal are transmitted through different transmission paths. Therefore, a transmission line for transmitting the audio signal or the control signal is required in addition to the transmission line for transmitting the video signal.
The present invention is made to solve the above-described problems and has for its object to provide a signal transmission system, a signal transmission apparatus, and a signal reception apparatus which are able to transmit an audio signal and a control signal together with a video signal through the same transmission path.